Specular masking support added

Added support for specular masking through the use of Specular texture added in TextureType. Texture mask is a grayscale image where black pixel allows for full specularity and white pixel completely masks out specularity. In other words, black mask is transparent and the light shines right through whereas white mask is opaque.

I needed this when I was rendering planets where only the oceans had to shine while the continents retained diffused look. I figure others may benefit from specular masking as well.

![Screenshot_2013-01-09-17-21-18](https://f.cloud.github.com/assets/3170805/52878/270a619e-5a36-11e2-9c21-8ba139a185f2.png)

Besides the specular masking, the class is essentially identical to BumpmapPhongMaterial.